Serial Determinations of Neutrophil CD64 Expression for the Diagnosis and Monitoring of Sepsis in Critically Ill Patients

Background. Early identification of sepsis is important to be able to initiate timely therapy and optimize survival. Neutrophil CD64 (nCD64) expression has been proposed as a potential marker of sepsis. Methods. In this prospective observational study, adult patients admitted to our 34-bed medico-surgical department of intensive care over a 3.5-month period were included. Neutrophil CD64 expression was measured by flow cytometry at admission and daily until discharge or death. Blood C-reactive protein (CRP) level was measured routinely. Diagnosis of sepsis was recorded and appropriateness of empirical antibiotic treatment was established post hoc. Results. Of the 548 patients included, 468 had flow cytometry measurements within 24 hours after admission, of whom 103 had sepsis. Septic patients had higher admission nCD64 expression than did nonseptic patients (P < .001). A cutoff admission nCD64 expression of 230 median fluorescence intensity (MFI) identified sepsis with a sensitivity of 89% (81%-94%) and specificity of 87% (83%-90%). When combining CRP and nCD64 expression, an abnormal result for both was associated with a 92% probability of sepsis, whereas sepsis was ruled out with a probability of 99% if both were normal. Septic patients receiving inappropriate empirical antibiotics had persistently elevated nCD64 expression, whereas expression decreased over time in patients receiving appropriate antibiotics. In nonseptic patients, an increase in nCD64 expression >= 40 MFI predicted intensive care unit (ICU)-acquired infection (n = 29) with a sensitivity of 88% and specificity of 65%. Conclusions. Measurement of nCD64 expression at ICU admission, especially when combined with CRP concentrations, is useful in diagnosing sepsis. Serial determinations of nCD64 could be used for monitoring purposes.